bug#35696: ; bug#35571; bug#36039

[Ikumi Keita]

Dear the bug reporters,

I just committed a "fix" for preview-latex in the git repository of
AUCTeX.  You can try it out at git://git.savannah.gnu.org/auctex.git .

Unfortunately, the latest development version offers only partial
solution if you are using gs 9.27.  Please read on for detail.

1. When you use gs 9.28 or later after gs 9.28 is released, customize
   `preview-pdf-color-adjust-method' to t.
   This includes the case that your (Linux or *BSD) binary package
   manager distributes gs 9.27 with necessary patches.
2. When you use gs 9.26 or before, customize
   `preview-pdf-color-adjust-method' to `compatible'.
3. When you use gs 9.27 and it doesn't have the necessary patches
   applied,
3-1. if you don't customize the foreground color of Emacs, customize
     `preview-pdf-color-adjust-method' to `compatible'.
3-2. if you customize the foreground color of Emacs and the background
     is light (i.e. not dark), customize
     `preview-pdf-color-adjust-method' to `compatible' and
     `preview-reference-face' to have default (black) foreground color.
3-3. if you customize the foreground color of Emacs and the background
     is dark, customize `preview-pdf-color-adjust-method' to nil.  This
     forces plain "black on white" appearance for the generated image.
     You can at least read what are written in the image although they
     may not match with your Emacs color well.

Best regards,
Ikumi Keita